Computer-generated video holograms can, for example, be reconstructed using a holographic display device as already described by the applicant in document WO 2004/044659. The observer looks towards the display screen through at least one virtual observer window, which is greater in size than an eye pupil.
An ‘observer window’ is a limited virtual region through which the observer can watch the entire reconstruction of the three-dimensional scene at sufficient visibility. The observer window is situated on or near the observer eyes. The observer window can be displaced in the x, y and z directions. Within the observer window, the wave fields interfere such that the reconstructed object becomes visible for the observer. The windows are situated near the observer eyes and can be tracked to the actual observer position with the help of known position detection and tracking systems. They can therefore preferably be limited to a size which is only a little larger than the size of the eye pupils. It is possible to use two observer windows, one for each eye. Generally, more complex arrangements of observer windows are possible as well. It is further possible to encode video holograms which contain objects or entire scenes which appear behind the SLM for the observer.
The term ‘transformation’ shall be construed to include any mathematical or computational technique which is identical to or which approximates a transformation. Transformations in a mathematical sense are merely approximations of physical processes, which are described more precisely by the Maxwellian wave equations. Transformations such as Fresnel transformations or the special group of transformations which are known as Fourier transformations, describe second-order approximations. Transformations are usually represented by algebraic and non-differential equations and can therefore be handled efficiently and at high performance using known computing means. Moreover, they can be used precisely in optical systems.
Document WO 2006/066919 A1 filed by the applicant describes a method for computing computer-generated video holograms. According to that method, objects with complex amplitude values of a three-dimensional scene are assigned to matrix dots of parallel virtual section layers such that for each section layer an individual object data set is defined with discrete amplitude values in matrix dots, and a holographic code for a light modulator matrix of a holographic display device is computed from the image data sets.
According to this invention, the solution of the object takes advantage of the general idea that the following steps are carried out aided by a computer:
A diffraction image is computed in the form of a separate two-dimensional distribution of wave fields for an observer plane, which is situated at a finite distance and parallel to the section layers, from each object data set of each tomographic scene section, where the wave fields of all sections are computed for at least one common virtual window, the observer window, which is situated in the observer plane near the eyes of an observer, the area of said observer window being smaller than the video hologram;
The computed distributions of all section layers are added to define an aggregated wave field for the observer window in a data set which is referenced in relation to the observer plane;
The reference data set is transformed into a hologram plane, which is situated at a finite distance and parallel to the reference plane, to create a hologram data set for an aggregated computer-generated hologram of the scene, where the light modulator matrix is situated in the hologram plane, and where the scene is reconstructed in the space in front of the eyes of the observer with the help of said light modulator matrix after encoding.
The above-mentioned methods and holographic display devices are based on the idea not to reconstruct the object of the scene itself, but preferably to reconstruct in one or multiple observer windows the wave front which would be emitted by the object.
The observer can watch the scene through the virtual observer windows. The virtual observer windows can be tracked to the actual observer position with the help of known position detection and tracking systems. A virtual, frustum-shaped reconstruction space stretches between the light modulator means of the holographic display device and the observer windows, where the SLM represents the base and the observer window the top of the frustum. If the observer windows are very small, the frustum can be approximated as a pyramid. The observer looks though the virtual observer windows towards the display and receives in the observer window the wave front which represents the scene.